The present invention relates to a recording apparatus for reproducing information recorded with density on a recording medium by utilizing near-field light.
In many of the existing information reproducing apparatuses, reproduction is being made of information recorded on a read-only optical disc such as CDs and CD-ROMs. For example the CD on its surface is recorded, as concave-and-convex formed information, with pits having a size nearly a wavelength of laser light to be used during reproduction and a depth of about one-fourth of that wavelength. The phenomenon of light interference is utilized in reproducing information.
Meanwhile, on the market are rewritable recording mediums adopting a scheme represented by a magneto-optical recording scheme and phase shift recording scheme, realizing high density information recording. For example, in the phase change recording scheme, laser light is illuminated to a recording medium formed on a surface with a phase change film to cause temperature at a laser light illumination spot. By changing the intensity of laser light, binary recording due to crystalline and amorphous forms has been feasible. The information thus recorded is reproduced by illuminating laser light to the recording medium with intensity lower than that of recording and distinguishing between a crystallization phase and an amorphous phase due to the intensity of its reflection.
In reproducing information recorded on the read-only optical disc, a lens optical system is used which has being employed for the conventional optical microscope. Due to limitation by light diffraction, it is impossible to reduce the spot size of laser light less than a half wavelength. Consequently, in the case of further increasing the information recording density of the optical disc, the pit size or track pitch is reduced and hence the information recording unit is reduced to a smaller size than the laser light wavelength. Thus, information reproduction is not feasible.
Meanwhile, in a recording medium recorded with information by the magneto-optical recording scheme and phase change recording scheme, information recording/reproduction with density is realized due to microscopic spot of laser light. Accordingly, the information recording density on the recording medium is limited to the spot size obtainable by focusing laser light. Accordingly, in the conventional optical information recording apparatus adopting a magneto-optical recording scheme and phase change recording scheme, it has been impossible to reduce the spot size obtained by focusing laser light to smaller than a laser light diffraction limit, i.e. a half wavelength of laser light.
On the other hand, there is a proposal of an information reproducing method/apparatus utilizing near-field light created through a microscopic aperture having a diameter smaller than a wavelength of utilized laser light, e.g. approximately {fraction (1/10)}th of the wavelength.
Conventionally, as an apparatus utilizing near-field light there has been a near-field microscope employing a microscopic aperture as above, being utilized for observing a microscopic surface structure of a sample. As one of near-field light utilizing schemes for the near-field microscope, there is a scheme (illumination mode) that the distance between a probe microscopic aperture and a sample surface is brought close to nearly a diameter of the probe microscopic aperture so that propagation light is introduced through the probe and directed to the probe microscopic aperture, thereby creating near-field light in the microscopic aperture. In this case, the created near-field light and the sample surface interact with to cause scattering light to be detected by a scattering light detecting system, accompanied by an intensity or phase reflecting a sample surface fine structure. Thus, observation is possible with high resolution not realizable by the conventional optical microscope.
Meanwhile, as another scheme of a near-field microscope utilizing near-field light, there is a scheme (collection mode) that propagation light is illuminated to a sample to localize near-field light on a sample surface whereby the probe microscopic aperture is brought close to the sample surface nearly to an extent of a diameter of the probe microscopic aperture. In this case, the localized near-field light and the probe microscopic aperture interact to cause scattering light to be introduced to a scattering light detecting system through the probe microscopic aperture, accompanied by an intensity or phase reflecting a sample surface fine structure. Thus, high resolution observation is realized.
The information reproducing method/apparatus utilizing near-field light as mentioned above utilizes these observation schemes for the near-field microscope.
Accordingly, the utilization of near-field light makes possible information reproduction (reading) from the information recording medium recorded exceeding the recording density on the conventional information recording medium.
In the meanwhile, in order to realize reproduction of information recorded on the recording medium through utilizing near-field light mentioned above, there is a necessity for probe proximity control technology to bring a probe microscopic aperture portion as an optical head and a surface of the recording medium to a fully-close distance of from several nano-meters to 10 nano-meters.
In the conventional hard disc technologies, there is a flying head technology to bring a recording head and a recording medium close to each other. The float amount of the flying head from a recording medium surface is about from 50 nano-meters to 100 nano-meters, which value is too great to realize information reproduction utilizing near-field light.
On the other hand, the scanning probe micros (SPM) represented by the scanning tunnel microscope (STM) or atomic force microscope (AFM) are used in order to observe nano-meter order microscopic regions on sample surfaces. The SPM uses a tip sharpened probe to detect a physical amount, such as a tunneling current or inter-atomic force caused between the probe and the sample surface, whereby scanning is made on the sample surface in proximity to the sample surface to obtain high resolution image.
Accordingly, this SPM probe proximity technology is applicable to a near-field microscope or a recording apparatus utilizing near-field light. Thus, the recording medium and the probe microscopic aperture at its tip can be kept in a fully closed state.
In this case, however, there arises a need to detect by respective unique mechanisms a physical amount replaced by information recorded on the recording medium, or near-field light, and a physical amount required to effect proximity control of the probe, or inter-atomic force, making complicated the overall apparatus structure.
Also, because the SPM probe proximity technology requires a sharpened tip for the probe, it is not necessarily an optimal method for the near-field microscopes using a flat-surface probe without having a sharpened tip or the recording apparatuses utilizing near-field light.
Meanwhile, near-field light mentioned above abruptly attenuates in a z direction provided that a line connecting between the probe and recording medium is defined as a z direction. Accordingly, if the probe deviates in position in the z direction from the recording medium surface due to a certain cause, this induces a variation in the output signal. The presence or absence of a data mark on the recording medium increases and decreases the output signal. Thus, there has been a problem that, when there is a change in the output signal, it cannot be reliably determined whether the change is due to the presence of the data mark or due to deviation in probe position in the z direction.
There is a method for controlling the probe z-direction position by mechanically vibrating the probe in the z direction to keep the amplitude constant. However, this result in giving a physical impact to the recording medium surface, incurring damage to the recording medium and probe. Meanwhile, there has been difficulty in reducing apparatus size due to probe vibration control and amplitude detecting mechanism.
Therefore, it is an object of the present invention to provide in view of the above-stated problems a recording apparatus to realize, with a simple structure, reproducing and recording information reliably for a recording medium having high density record.
In order to achieve the above object, a recording apparatus according to the present invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, characterized in that: light is illuminated to the recording medium to create near-field light on a surface of the recording medium, and a probe having a microscopic aperture being brought into proximity to the surface of the recording medium; an intensity of propagation light being detected to control a distance between the microscopic aperture and the recording medium based on the intensity of the propagation light.
Accordingly, achieved is reproduction of high density information recorded on a recording medium by utilizing near-field light. Simultaneously, similarly utilizing near-field light, control is possible for a distance between the microscopic aperture of the aperture element and the recording medium.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having a microscopic aperture to create or scatter near-field light; a light illuminating means for illuminating illumination light to the recording medium such that near-field light is created on a surface of the recording medium; a light detecting means for detecting propagation light caused by scattering the near-field light by the microscopic aperture to turning this into a reproduced signal; a control means for controlling a spacing between the aperture element and the recording medium based on the reproduced signal.
Accordingly, achieved is reproduction of high density information recorded on a recording medium by utilizing near-field light. Simultaneously, from the reproduced signal a distance control signal representative of a distance between the microscopic aperture of the aperture element and the recording medium can be obtained by the distance control signal deriving means. Based on the distance control signal, the aperture element and the recording medium can be held in a proximity state.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having a microscopic aperture to create or scatter near-field light; a light illuminating/recording means for introducing illumination light to the microscopic aperture such that near-field light is created in the microscopic aperture; a light detecting means for detecting propagation light caused by scattering the near-field light by the recording medium to turning this into a reproduced signal; a control means for controlling a spacing between the aperture element and the recording medium based on the reproduced signal.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium in a proximity state can be made both by utilizing near-field light. Also, by comparatively increasing the intensity of illumination light introduced to the microscopic aperture, intense near-field light can be created. Localized thermal energy illumination makes possible also information recording.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having a microscopic aperture to create or scatter near-field light; a light illuminating means for illuminating illumination light having a definite wavelength width or a plurality of wavelengths to the recording medium such that near-field light is created on a surface of the recording medium; a scattering light detecting means for detecting scattering light caused as a result of interaction of the near-field light with the recording medium or the aperture element correspondingly to the wavelength of the illumination light; a control means for controlling a spacing between the aperture element and the recording medium based on the scattering light.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium in a proximity state can be made both by utilizing near-field light. Furthermore, it is possible to positively separate a reproduced signal and a distance control signal for performing proximity control on the aperture element, by utilizing and assigning different wavelengths respectively to the illumination light used to reproducing information recorded on the reproducing medium and the illumination light used to perform proximity control on the aperture element. Also, because scattering light is detected correspondingly to different wavelengths of illumination light, distance information about the reproduce probe and information recording medium is obtained by utilizing the difference of scattering light intensity in dependence upon the illumination light wavelength. Information reproduction and control of the probe in the z-axis direction position can be made without vibration of the probe in the z-axis direction. This makes unnecessary the probe z-direction vibration mechanism and z-axis amplitude detecting mechanism, making possible simple apparatus structure. Also, distance control makes unnecessary the detection of a signal peak. Also, because there is no physical contact of the probe with the information recording medium, reduced is damage to the probe and information recording medium.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having a microscopic aperture to create or scatter near-field light; a light illuminating/recording means for illuminating illumination light having a definite wavelength width or a plurality of wavelengths to the microscopic aperture such that near-field light is created in the microscopic aperture, and recording information to the recording medium through illumination light having one of the plurality of wavelengths; a scattering light detecting means for detecting scattering light caused as a result of interaction of the near-field light with the recording medium or the aperture element correspondingly to the wavelength of the illumination light; a control means for controlling a spacing between the aperture element and the recording medium based on the scattering light.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium in a proximity state can be made both by utilizing near-field light. Further, it is possible to positively separate a reproduced signal and a distance control signal for performing proximity control on the aperture element, by utilizing and assigning different wavelengths respectively to the illumination light used to reproducing information recorded on the reproducing medium and the illumination light used to perform proximity control on the aperture element. Also, by comparatively increasing the intensity of illumination light introduced to the microscopic aperture, intense near-field light can be created. Localized thermal energy illumination makes possible also information recording.
Also, a recording apparatus according to the invention is, in any one invention of claim 4 or 5, the plurality of wavelength of the illumination light is switched in time.
Accordingly, compact apparatus structure is feasible due to emitting a plurality of wavelengths of light by the single light source.
Also, a recording apparatus according to the invention is, in any one invention of claim 4 or 5, the scattering light detecting means has a selection wavelength to be switched in time.
Accordingly, compact apparatus structure is feasible due to receiving the scattering light by the single light receiving element, in addition to the effect of claim 4 or 5.
Also, a recording apparatus according to the invention is, in any one invention of claim 4 or 5, the wavelength of the illumination light is plurality in number to be simultaneously inputted.
Accordingly, further compact apparatus structure is feasible because of unnecessity of a mechanism to select an input light wavelength, in addition to the effect of claim 4 or 5.
Also, a recording apparatus according to the invention is, in any one invention of claim 4 or 5, the scattering light detecting means has a plurality of light receiving means to receive correspondingly to respective ones of different wavelengths of the illumination light.
Accordingly, the wavelength selecting means is simplified and hence compact apparatus structure is feasible, because the unnecessity of switching in time between selective wavelengths when the light receiving element receives scattering light.
Also, a recording apparatus according to the invention is, in any one invention of claim 4 or 5, the illumination light comprises a plurality of wavelength components, the illumination light having a definite width of a wavelength width with respect to respective ones of the plurality of wavelengths.
Accordingly, in addition to the effect of claim 4 or 5, because the input means allows the input light wavelength to have a width, increased are the kinds of input means to be utilized. As a result, the kinds of wavelengths are increased to be utilized. This makes it easy to utilize a wavelength for accurately control the distance between the probe and the information recording medium.
Also, a recording apparatus according to the invention is, in any one invention of claim 4 or 5, the illumination light has a wavelength having a definite width, a wavelength selecting means selecting one part of the width.
Accordingly, in addition to the effect of claim 4 or 5, simpler structure is realized because the input light must not be limited in wavelength, such as to laser.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having a microscopic aperture to create or scatter near-field light; a light illuminating means for illuminating lillumination light mixed with two different modulation frequency light to the recording medium such that near-field light is created on a surface of the recording medium; a first light detecting means for scattering the created near-field light by the microscopic aperture and detecting propagation light having one of the two modulation frequencies, turning this into a reproduced signal; a second light detecting means for scattering the created near-field light by the microscopic aperture and detecting propagation light having the other of the two modulation frequencies, turning this into a control signal; a control means for controlling a spacing between the aperture element and the recording medium based on the control signal.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium can be held in a proximity state both by utilizing near-field light. Furthermore, it is possible to positively separate a reproduced signal and a distance control signal for performing proximity control on the aperture element, by utilizing and assigning different wavelengths respectively to the illumination light used to reproducing information recorded on the reproducing medium and the illumination light used to perform proximity control on the aperture element.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having a microscopic aperture to create or scatter near-field light; a light illuminating/recording means for illuminating illumination light mixed with two different modulation frequencies to the microscopic aperture to create near-field light in the microscopic aperture, and recording information to the recording medium through illumination light having one of at least the two modulation frequencies; a first light detecting means for scattering the created near-field light by the microscopic aperture and detecting propagation light having one of the two modulation frequencies, turning this into a reproduced signal; a second light detecting means for scattering the created near-field light by the microscopic aperture and detecting propagation light having the other of the two modulation frequencies, turning this into a control signal; a control means for controlling a spacing between the aperture element and the recording medium based on the control signal.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium in a proximity state can be made both by utilizing near-field light. Furthermore, it is possible to positively separate a reproduced signal and a distance control signal for performing proximity control on the aperture element, by utilizing and assigning different wavelengths respectively to the illumination light used to reproducing information recorded on the reproducing medium and the illumination light used to perform proximity control on the aperture element. Also, by comparatively increasing the intensity of illumination light introduced to the microscopic aperture, intense near-field light can be created. Localized thermal energy illumination makes possible also information recording.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having two microscopic apertures to create or scatter near-field light; a light illuminating means for illuminating illumination light to the recording medium such that near-field light is created on a surface of the recording medium; a first light detecting means for detecting propagation light caused by scattering the near-field light by one of the microscopic apertures, turning this into a reproduced signal; a second light detecting means for detecting propagation light caused by scattering the near-field light by the other of the microscopic apertures, turning this into a control signal; a control means for controlling a spacing between the aperture element and the recording medium based on the control signal.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium in a proximity state can be made both by utilizing near-field light. Furthermore, because the aperture element is formed independently with a microscopic aperture used to reproduce information recorded on the recording medium and a microscopic aperture used to perform proximity control of the aperture element, it is more positively separate a reproduced signal and a distance control signal for performing proximity control of the aperture element.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having two microscopic apertures to create or scatter near-field light; a first light illuminating means for illuminating illumination light to the recording medium such that near-field light is created on a surface of the recording medium; a second light illuminating/recording means for illuminating illumination light to one of the microscopic apertures such that near-field light is created in the microscopic aperture; a first light detecting means for detecting propagation light caused by scattering the near-field light by one of the microscopic apertures, turning this into a reproduced signal; a second light detecting means for detecting propagation light caused by scattering the near-field light by the other of the microscopic apertures, turning this into a control signal; a control means for controlling a spacing between the aperture element and the recording medium based on the control signal.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium in a proximity state can be made both by utilizing near-field light. Furthermore, because the aperture element is formed independently with a microscopic aperture used to reproduce information recorded on the recording medium and a microscopic aperture used to perform proximity control of the aperture element, it is more positively separate a reproduced signal and a distance control signal for performing proximity control of the aperture element. Furthermore, by comparatively increasing the intensity of illumination light introduced to the microscopic aperture by the second light illuminating means, intense near-field light can be created. Localized thermal energy illumination makes possible also information recording.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having two microscopic apertures to create or scatter near-field light; a light illuminating/recording means for introducing illumination light to one of the microscopic apertures such that near-field light is created in the microscopic aperture; a light illuminating means for introducing illumination light to the other of the microscopic apertures such that near-field light is created in the microscopic aperture; a first light detecting means for detecting propagation light caused by scattering the near-field light by one of the microscopic apertures, turning this into a reproduced signal; a second light detecting means for detecting propagation light caused by scattering the near-field light by the other of the microscopic apertures, turning this into a control signal; a control means for controlling a spacing between the aperture element and the recording medium based on the control signal.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium in a proximity state can be made both by utilizing near-field light. Furthermore, because the aperture element is formed independently with a microscopic aperture used to reproduce information recorded on the recording medium and a microscopic aperture used to perform proximity control of the aperture element, it is more positively separate a reproduced signal and a distance control signal for performing proximity control of the aperture element. Furthermore, by comparatively increasing the intensity of illumination light introduced to the microscopic aperture, intense near-field light can be created. Localized thermal energy illumination makes possible also information recording.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having two microscopic apertures to create or scatter near-field light; a light illuminating/recording means for introducing illumination light to one of the microscopic apertures such that near-field light is created in the microscopic aperture; a light illuminating means for illuminating illumination light to the other of the microscopic apertures such that near-field light is created in the microscopic aperture; a first light detecting means for detecting propagation light caused by scattering the near-field light by one of the microscopic apertures, turning this into a reproduced signal; a second light detecting means for detecting propagation light caused by scattering the near-field light by the other of the microscopic apertures, turning this into a control signal; a control means for controlling a spacing between the aperture element and the recording medium based on the control signal.
Accordingly, reproduction of high density information recorded on the recording medium and holding the aperture element and the recording medium in a proximity state can be made both by utilizing near-field light. Furthermore, because the aperture element is formed independently with a microscopic aperture used to reproduce information recorded on the recording medium and a microscopic aperture used to perform proximity control of the aperture element and further near-field light is formed by different creating methods that is utilized for reproducing information recorded on the recording medium and proximity control of the aperture element to the recording medium, it is more positively separate and detect a reproduced signal and a distance control signal for performing proximity control of the aperture element without interference between the respective ones of near-field light. Furthermore, by comparatively increasing the intensity of illumination light introduced to the microscopic aperture, intense near-field light can be created. Localized thermal energy illumination makes possible also information recording.
Also, a recording apparatus according to the invention is, in any one invention of claims 14 to 17, the aperture element is provided with a step in a thickness direction to have a first bottom surface and a second bottom surface, the first bottom surface being provided with the one of microscopic apertures, the second bottom surface being provided with the other of microscopic apertures; the control means calculating a relative value of the reproduced signal detected by the first light detecting means and the signal detected by the second light detecting means, and controlling the spacing between the aperture element and the recording medium based on the relative value.
Accordingly, the provision of a step in the bottom surface of the aperture element causes difference in intensity of propagation light to be detected. A relative value of between signals to be detected by the respective two microscopic apertures is used as a distance control signal for performing proximity control of the aperture element. Accordingly, even where for example the information on the recording medium cannot be fully detected and hence an intense reproduced signal cannot be obtained, the distance control signal is used as a ratio to the reproduced signal to thereby stably obtain an intensity. Thus, reliable proximity control of the aperture element can be made.
Also, a recording apparatus of the invention is, in a recording apparatus for reproducing information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having a microscopic aperture to create or scatter near-field light; a light illuminating means for illuminating illumination light to the recording medium such that near-field light is created on a surface of the recording medium; a light detecting means for detecting propagation light caused by scattering the near-field light by the microscopic aperture; a vertical fine vibrating means for causing the microscopic aperture in a thickness direction of the aperture element; a control means for rendering as a reproduced signal a signal detected by the light detecting means when the microscopic aperture reaches a desired height due to the vertical fine vibrating means and as a to-be-operated signal a signal detected by the light detecting means when the microscopic aperture reaches a point above the desired height due to the vertical fine vibrating means, and calculating a relative value of the reproduced signal and the to-be-operated signal to control a spacing between the aperture element and the recording medium based on the relative value.
Accordingly, the vertical vibration of one microscopic aperture changes a position scattering near-field light. Because a relative value of a signal to be detected at a desired height of the microscopic aperture, i.e. reproduced signal, and a signal to be detected at an above point than the desired height of the microscopic aperture, i.e. to-be-detected signal, is used as a distance control signal. Accordingly, even where for example the information on the recording medium cannot be fully detected and hence an intense reproduced signal cannot be obtained, the distance control signal is used as a ratio to the reproduced signal to thereby stably obtain an intensity. Thus, reliable proximity control of the aperture element can be made.
Also, a recording apparatus according to the invention is, in a recording apparatus for reproducing or recording information recorded on a recording medium by utilizing near-field light, the recording apparatus, comprising: an aperture element having a microscopic aperture to create or scatter near-field light; a light illuminating/recording means for introducing illumination light to the microscopic aperture such that near-field light is created in the microscopic aperture; a light detecting means for detecting propagation light caused by scattering the near-field light by the microscopic aperture; a vertical fine vibrating means for causing the microscopic aperture in a thickness direction of the aperture element; a control means for rendering as a reproduced signal a signal detected by the light detecting means when the microscopic aperture reaches a desired height due to the vertical fine vibrating means and as a to-be-operated signal a signal detected by the light detecting means when the microscopic aperture reaches a point above the desired height due to the vertical fine vibrating means, and calculating a relative value of the reproduced signal and the to-be-operated signal to control a spacing between the aperture element and the recording medium based on the relative value.
Accordingly, the vertical vibration of one microscopic aperture changes a position scattering near-field light. Because a relative value of a signal to be detected at a desired height of the microscopic aperture, i.e. reproduced signal, and a signal to be detected at an above point than the desired height of the microscopic aperture, i.e. to-be-detected signal, is used as a distance control signal. Accordingly, even where for example the information on the recording medium cannot be fully detected and hence an intense reproduced signal cannot be obtained, the distance control signal is used as a ratio to the reproduced signal to thereby stably obtain an intensity. Thus, reliable proximity control of the aperture element can be made. Furthermore, by comparatively increasing the intensity of illumination light introduced to the microscopic aperture, intense near-field light can be created. Localized thermal energy illumination makes possible also information recording.
Also, a recording apparatus according to the invention is, in any one invention of claims 1 to 20, further comprising a horizontal fine vibrating means for causing the aperture element to finely vibrate in a direction perpendicular to a direction of arrangement of information units recorded on the recording medium and a direction parallel with a surface of the recording medium, and a position control means for controlling a position of the aperture element such that the reproduced signal becomes a maximum in a vibration center of fine vibration due to horizontal fine vibrating means.
Accordingly, made possible is position control in a direction perpendicular to a direction of arranging information units on the recording medium and parallel with the recording medium surface, i.e. tracking control. Because this tracking control provides a stable reproduced signal, proximity control utilizing this reproduced signal is also positive, thus improving reliability of information reproduction.